The canteen (water bottle) is normally part of the whole webbing assembly used by the Brits. It would be attached to the ends of the cross straps and be positioned on the right hip. If, if, for whatever reason one wished to lug along a water bottle on it’s own, it could be attached to a single cross strap and carried slung wherever; so being merciful to the modeller, who may not be well-versed in much of this at all, one could, just about, find a discarded water bottle thus.